re PR tree-optimization/38785 (huge performance regression on EEMBC bitmnp01)

re PR tree-optimization/38785 (huge performance regression on EEMBC bitmnp01)

	PR tree-optimization/38785
	* common.opt (ftree-partial-pre): New option.
	* doc/invoke.texi: Document it.
	* opts.c (default_options_table): Initialize flag_tree_partial_pre.
	* tree-ssa-pre.c (do_partial_partial_insertion): Insert only if it will
	benefit speed path.
	(execute_pre): Use flag_tree_partial_pre.

Co-Authored-By: Maxim Kuvyrkov <maxim@codesourcery.com>
Co-Authored-By: Steven Bosscher <steven@gcc.gnu.org>
From-SVN: r186928